The Semiautomatic Reid Vapor Pressure Apparatus (RVP 100) was developed to save operator's time in carrying out vapor pressure testing of gasoline, to reduce the variables inherent in the standard method, and to improve repeatability of test results. The standard American Society of Testing Materials (ASTM) test methods D323 and D4953 specify that a standard gasoline chamber, sometimes referred to as a "test bomb", is filled with a chilled sample connected to an air chamber, and immersed in a constant temperature bath at 100.degree. F. The apparatus is periodically removed from the bath and shaken until a constant pressure is observed on a gauge attached to the air chamber. After each test, gauge calibration must be checked, with the total test time involved typically being on the order of 20-30 minutes.
A later Reid Vapor Pressure Apparatus was developed to meet the requirements of ASTM standard test methods D323 and D4953, in which the standard gasoline chambers filled with the sample to be tested are coupled to air chambers as specified in the aforementioned test methods to form a vapor pressure "bomb". The assembled vapor pressure bombs are then tilted 20.degree. to 30.degree. with the upper end extending downward to transfer some of the sample into the vapor chamber. The test bomb is then placed horizontally in a constant temperature bath and rotated slowly in 180.degree. clockwise and 180.degree. counterclockwise cycles about its longitudinal axis. Although this has shortened the period for achieving thermal equilibrium, it has also resulted in gasoline flowing into the tube leading to the pressure gauge which interferes with and limits the accuracy of the vapor pressure measurements.
The present invention overcomes the aforementioned limitations of the prior art by providing apparatus for measuring the vapor pressure of a volatile liquid which continuously shakes one or more pressure test chambers in a constant temperature bath by moving a tray on which the test chambers are positioned in a reciprocating manner. There is no need for the operator to tilt the test chambers downward to insure sample transfer from the liquid chamber to the vapor chamber. The test chamber is placed horizontally in a constant temperature bath. Some of the sample is transferred from the liquid chamber to the vapor chamber during vigorous reciprocating movement of the test chambers during the test. Handling of the pressure test chambers during testing is eliminated, freeing an operator to perform other work after the test is initiated. Thermal equilibrium is achieved in a very short time, expediting vapor pressure testing, and the liquid under test remains isolated from the pressure transducer.
Accordingly, it is an object of the present invention to provide improved apparatus for measuring the vapor pressure of a volatile liquid.
Yet another object of the present invention is to quickly and accurately measure the vapor pressure of a volatile petroleum product such as gasoline at a predetermined, fixed temperature and using conventional test chambers in accordance with ASTM standard test methods, D323, D4953.
A further object of the present invention is to quickly bring a liquid in a closed chamber to a fixed, predetermined temperature for measuring the vapor pressure of the liquid at the predetermined temperature.
The present invention contemplates apparatus for measuring the vapor pressure of a volatile liquid comprising: one or more closed test chambers each including a first section containing a liquid and a second section coupled to the first section; a constant temperature source coupled to the test chambers for maintaining the liquid in each of the test chambers at a predetermined, fixed temperature; a moveable tray coupled to the test chambers; drive means coupled to the moveable tray for linearly displacing the moveable tray and the test chambers in a reciprocating manner for transferring a portion of the liquid from the first section to the second section of each of the test chambers and for rapidly bringing the temperature of the liquid to the predetermined, fixed temperature in stabilizing the vapor pressure of the liquid at a constant value; and vapor pressure measuring and indicator means coupled to the second section of each of the test chambers and responsive to the vapor pressure of the liquid therein for displaying the vapor pressure of the liquid at the predetermined, fixed temperature.